VoLTE (Voice over Long Term Evolution) is emerging as the preferred solution for the need to support real time voice traffic in IP networks.
The move towards all-IP and Voice over Internet Protocol (VoIP) in wireless access networks (such as, LTE)) will dramatically increase overhead due to headers. For example, VOIP is be carried by the Real-time Transport Protocol/User Datagram Protocol/Internet Protocol (RTP/UDP/IP) suite. Assuming a cellular codec encoding rate of 12.2 kbps (kilobits per second), there is a payload (voice packets) of 34 bytes and a header overhead of 40 bytes for RTP/UDP/IPv4 (in case of IP version four). This is an enormous overhead, and is clearly an unacceptable use of precious wireless bandwidth. This is especially true because, for VoIP, each User Equipment (UE) sends one RTP/UDP/IP frame every 20 ms (milliseconds). Further, these header fields do not change throughout the packet stream. Hence, these RTP/UDP/IP headers are compressed using a Robust Header Compression (ROHC) scheme, which is enabled by the network operator during the VoLTE call for compression of the header fields (which may otherwise lead to enormous overhead).
During the VoLTE call, the network can enable the ROHC scheme on all the voice packets sent by the UE. A ROHC compressor in the UE can compress the RTP/UDP/IP headers to minimum of 4 bytes of Header and sends to the ROHC decompressor (which is present at the receiver side in the UE).
In an existing system, during the VoLTE call, most of the Transport Control Protocol/Internet Protocol (TCP/IP) stacks (such as android TCP/IP stack or windows TCP/IP stack and the like) generate IP Identification (IP-ID) attribute in the IP header as zero. Further, the IP-ID is dependent on application type for generating IP-ID by TCP/IP stack. During the VoLTE call, the IP-ID is static with value zero. When the IP-ID is zero, the ROHC compressor sends the IP-ID uncompressed value. The IP-ID is generally two bytes and these two bytes of IP-ID is added to the compressed four bytes by the ROHC compressor. In the existing system, each time the ROHC compressor in the UE adds the IP-ID (without compression) to the compressed four bytes of packet data. Due to this, there is an overhead of two bytes of data for each ROHC compressed data (which is four bytes). This overhead of two bytes is consuming the precious bandwidth and the Radio resources between the UE and the Evolved Node B (eNB). In the existing system, there is no mechanism to indicate the static IP-ID (IP-ID with value zero) when a ROHC context is enabled.